A. Field of the Invention
The present invention relates generally to photonic crystals, and, more particularly to electro-optical switching using coupled photonic crystal waveguides.
B. Description of the Related Art
During the last decade photonic crystals (also known as photonic bandgap or PBG materials) have risen from an obscure technology to a prominent field of research. In large part this is due to their unique ability to control, or redirect, the propagation of light. E. Yablonovich, “Inhibited spontaneous emission in solid-state physics and electronics,” Physical Review Letters, vol. 58, pp. 2059-2062 (May 1987), and S. John, “Strong localization of photons in certain disordered dielectric superlattices,” Physical Review Letters, vol. 58, pp. 2486-2489 (June 1987) initially proposed the idea that a periodic dielectric structure can possess the property of a bandgap for certain frequencies in the electromagnetic spectra, in much the same way as an electronic bandgap exists in semiconductor materials. This property affords photonic crystals with a unique ability to guide and filter light as it propagates within it. Thus, photonic crystals have been used to improve the overall performance of many optoelectronic devices.
The concept of a photonic bandgap material is as follows. In direct conceptual analogy to an electronic bandgap in a semiconductor material, which excludes electrical carriers having stationary energy states within the bandgap, a photonic bandgap in a dielectric medium excludes stationary photonic energy states (i.e., electromagnetic radiation having some discrete wavelength or range of wavelengths) within that bandgap. In semiconductors, the electronic bandgap results as a consequence of having a periodic atomic structure upon which the quantum mechanical behavior of the electrons in the material must attain eigenstates. By analogy, the photonic bandgap results if one has a periodic structure of a dielectric material where the periodicity is of a distance suitable to interact periodically with electromagnetic waves of some characteristic wavelength that may appear in or be impressed upon the material, so as to attain quantum mechanical eigenstates.
A use of these materials that can be envisioned, is the optical analog to semiconductor behavior, in which a photonic bandgap material, or a plurality of such materials acting in concert, can be made to interact with and control light wave propagation in a manner analogous to the way that semiconductor materials can be made to interact with and control the flow of electrically charged particles, i.e., electricity, in both analog and digital applications.
Planar photonic crystal circuits such as splitters, high Q-microcavities, and multi-channel drop/add filters have been investigated both theoretically and experimentally in both two- and three-dimensional structures. For two-dimensional photonic crystal structures, the photonic crystal will be either perforated in an infinitely thick dielectric slab or formed of infinitely long dielectric rods. In-plane light confinement is achieved in such structures by multiple Bragg reflections due the presence of the photonic crystal. For three-dimensional photonic crystal structures, confinement in vertical direction is achieved by total internal reflection (TIR).
Work on photonic crystal waveguided components is now moving towards the development of photonic bandgap integrated circuits (PBGICs) in which a variety of active and passive optical components are integrated monolithically on a chip. Electro-optical switches are key components of such PBGICs, yet only one proposal for implementing such switches—a resonator device—has appeared in the literature. See S. Fan et al., “High Efficiency Channel drop filter with Absorption-Induced On/Off Switching and Modulation,” USA (2000).
Thus, there is a need in the art for an electro-optical switching device for PBGICs that addresses the needs of the related art.